The present invention relates to a disk drive with enhanced reliability resulting from improved error recovery procedures.
A disk drive using a magnetic disk as a recording medium utilizes a head to read and write data from/on a magnetic disk. The actual transducer elements which are referred to as the head(s) are disposed in a slider which has an air bearing surface facing the magnetic disk. The slider is provided at an end of the head arm, which is rotated by a rotary actuator to move the head slider in an approximately radial direction of the magnetic disk.
Further, an elastic member disposed on the head arm exerts a force on the slider toward the magnetic disk. If air flows between the head slider and the magnetic disk as the magnetic disk rotates, the slider flies up from a surface of the magnetic disk against the force exerted by the elastic member. The spacing between the magnetic disk and the head slider is determined on the basis of various conditions including the relative speed of the air bearing face and the magnetic disk.
A surface of a magnetic disk may have some unwanted projections (asperities), for example, due to reduced precision in manufacturing.
When the head hits a projection of the magnetic disk, the head is abruptly heated as a result of frictional heating or the like. This is called a thermal asperity. Especially in a head using a magnetoresistive (MR) element or a giant magnetoresistive (GMR) element, an increase in head temperature will lead to a great change in a read signal, significantly degrading the read/write reliability and, in some cases, making it impossible to read/write data from/on the magnetic disk.
As the recording density is increased, the distance between the recording surface and the head is decreased. Thus, the possibility that the head will strike such microscopic projections increases.
Some conventional disk drives take measures such as correcting variations in a head output due to variations in temperature utilizing the direct-current component of the read output of the head or the like or reducing the low-frequency component of the read output of the head, so that the influence of a thermal asperity is lowered to allow normal reading and writing.
Since a particular thermal asperity may grow with the passage of time, it may not be desirable to continue using a sector on the disk having a thermal asperity for reliability.
The conventional disk drive also takes measures to reduce the effect of a thermal asperity in service, but does not take any positive measures to detect thermal asperities. Such apparatus is susceptible of improvement in terms of reliability.
To solve the above problem, a disk drive according to the present invention has recording medium; at least one head for reading information from said recording medium; a signal filter for filtering a selected set of frequencies from an output from the head when the signal filter is turned on; switching means for the signal filter which allows the signal filter to be turned off or on; an error detection means for detecting an error occurring in a first region when read by the head with the signal filter turned on; and an error processing means for executing a plurality of error recovery procedures when an error is detected by said error detection means, one of the error recovery procedures including thermal asperity detection by turning off the signal filter and using a signal from the head which has not been filtered by the signal filter to determine whether the error is caused by a thermal asperity, and if the error is caused by a thermal asperity, assigning an alternate region for first region.
Further, the recovery means may include a position detection means for detecting a position of the error; and the error processing means may register the region in which the error occurs as the defective region when errors are repeatedly detected on the basis of a detection signal output from the position detection means for a predetermined number of times in the same position.
Furthermore, a method of executing an error recovery procedure in a disk drive according to the present invention comprises the steps of: detecting an error occurring in reading a first region with a head while a signal filter is turned on and filters a selected set of frequencies from an output from the head; rereading the first region with the signal filter switched off and using an unfiltered signal from the head to judge whether the error is caused by a thermal asperity; and if the error is caused by a thermal asperity, assigning an alternate region for first region. The method may also include rereading the first region a plurality of times while counting errors occurring at each position in the region; and if a count of errors at any single position exceeds a selected threshold, flagging the first region as having a thermal asperity.